Marine environment measuring sensors are sensors that measure a marine environment (see, for example, Patent Literatures 1 and 2). Examples of the measurement target of such marine environment measuring sensors are a seawater temperature, an earthquake motion, and undersea sound.
In order to maintain the measurement by the marine environment measuring sensor for a long time, it is necessary to secure power needed for such measurement for a long time. Hence, it is typical that the marine environment measuring sensor is provided with a primary battery or a secondary battery like a battery. Moreover, power is supplied to the marine environment measuring sensor arranged at an ocean bottom from the station building on the land, i.e., the power equipment provided at the land station in some cases. Furthermore, with a presumption that the marine environment measuring sensor is used near the ocean surface, there is proposed a technology of obtaining power through power generation utilizing ocean waves and solar light (see, for example, Patent Literatures 3, 4, and 5).
Furthermore, various power generating systems utilizing fluid force, such as the flow of a river, an ocean stream, and a tidal stream have been proposed, and some of such systems are already in practical use.
Regarding the power generation scheme of such power generating systems, it is typical to generate power by converting the fluid force into a rotational motion through a water wheel, and by rotating a power generator by a rotary force generated by such a rotational motion. This scheme is widely used as a hydroelectric power generation on the land. Moreover, this scheme is gradually applied to power generating equipment like tidal stream power generators in the case of ocean. For example, there is proposed a configuration for a power generating system which provides a dam on the land and provides a baffle structure or a wing in the ocean, thereby causing the taken fluid to contact a water wheel efficiently (see, for example, Patent Literature 6).
Conversely, a power generating system is examined which directly converts the energy of fluid force into power with a simple construction. In particular, in recent days, there is proposed a power generating scheme of utilizing force received by a column from a fluid.
For example, a column is arranged in the flow of a fluid, the column is caused to generate a Karman vortex, and vibration received by the column itself from the Karman vortex is transferred to a piezoelectric oscillator or an electromagnetic power generating mechanism, thereby obtaining power (see, for example, Patent Literature 7).
Moreover, there is proposed a scheme of obtaining power by transferring vibration produced at a column to a piezoelectric oscillator through a plate or the like (see, for example, Patent Literature 8).
Furthermore, there is proposed a scheme of arranging a cylindrical body in the flow of a fluid, of generating a Karman vortex behind such cylindrical body, and of utilizing a phenomenon that promotes, because of the Karman vortex, vibration of another cylindrical body provided so as to cross the former cylindrical body at right angle (see, for example, Patent Literature 9). According to this scheme, it is possible to generate power efficiently in a wide fluid velocity range.
Conversely, there is proposed a scheme of letting a vibrating plate pasted on a piezoelectric oscillator directly exposed to a fluid, and of causing the vibrating plate to vibrate (see, for example, Patent Literature 10).
As explained above, various power generating systems have been proposed, but currently, under a severe environment like an ocean, a scheme of obtaining a rotational motion from, for example, a tide stream using a water wheel and of generating power by rotating a power generator by such rotational motion is still popular.
Note that there is proposed a technology of measuring a flow rate by causing a column to produce a Karman vortex although it does not generate power (see, for example, Patent Literature 11).